In the past, in the field of adhesives and sealing materials, foam melt applicators for coating a foamable melted material have been known. See Japanese Document No. JP S59-182825A. A foam melt applicator is a device which mechanically mixes an inert gas into melted hot melt and discharges a bubbly hot melt. Coating a foamable melted material can reduce running costs and lengthen open time before clamping. Other effects include shortening the setting time after clamping, making it easier to thinly spread an adhesive layer after clamping, increased adhesion strength with porous materials, increased filling efficiency on a bonded item that has a rough surface, formation of a coating film with elasticity, etc. Therefore foamable melted materials are widely used.
For example, there is a device and method which manufacture an insulated plate by spreading foaming-type hot melt from a slot nozzle onto a long narrow band of material that is continuously transported, and gluing another long narrow band of material thereon. See Japanese Document No. JP S57-11440A.
Also, in order to prevent premature foaming of a foamable melted material inside a slot nozzle, there is a slot nozzle which can keep a foamable melted material at a pressure higher than the critical pressure at which the foamable melted material does not foam until the foamable melted material reaches the outlet part of the slot. See Japanese Document No. JP H7-308618A. This slot nozzle is provided with a converging slot part in which the thickness of the slot is gradually reduced from the wide slot part, where the slot is thick, to the outlet slot part, where the slot is thin.
To coat a foamable melted material in a wide band one must use a slotted discharge device. When one attempts to discharge foamable melted material with a slotted discharge device, many intrinsic problems occur.